U.S. Pat. No. 1,963,105 discloses the production of copper(I) oxide in a process in which copper metal suspended in water is subjected to the action of an oxygen-containing gas with agitation and at temperatures between 50.degree. and 100.degree. C. The reaction is promoted by an addition of alkali or alkaline earth metal halides. The product is used as paint for ships.
British Patent Specification 772,846 discloses the production of copper(I) oxide in a process in which an oxygen-containing gas acts on small-lump copper metal, which is suspended in an aqueous mineral acid, at temperatures not below 90.degree. C. and with agitation and while a gauge pressure of 0 to 6 atmospheres is maintained.
The known processes virtually always result in the formation of red copper(I) oxide although changes in color and in particle size from 1 to 3 micrometers can be effected by an addition of adjuvants and a change of the pressure and temperature.